1. Field of the Invention
This invention relates generally to novel methods of preparing crystalline molecular sieve materials, including FAU and LTH zeolites, as well as aluminum phosphate molecular sieves. By this improved method, novel molecular sieves are prepared having encapsulated multidentate metal chelate complexes which are incorporated internally of the sieve in a stable fashion.
2. Description of the Related Art
Molecular sieves of the crystalline zeolite type as well as the aluminum phosphate type are well known in the art and now comprise hundreds of species of both naturally occurring and synthetic compositions. In general, the crystalline zeolites are aluminosilicate frameworks based on an infinitely extending three-dimensional network of SiO.sub.4 and [AlO.sub.4 ].sup.-1 tetrahedra linked through common oxygen atoms. The framework structure encloses cavities occupied by large ions and water molecules, both of which have considerable freedom of movement, permitting ion exchange and reversible dehydration. The aluminum phosphate molecular sieves are similar structures comprised of [AlO.sub.4 ].sup.-1 and [PO.sub.4 ].sup.+1 tetrahedra linked through common oxygen atoms. Molecular sieves are attractive as interactive support materials because of their structural features and physical properties. These materials can provide shape selectively, ion exchange, acid-base sites, and large electrostatic fields.
In general, zeolites may be divided into ten different structural types depending on the structural building blocks. These groups include the analcime group, natorlite group, chabazite group, phillipsite group, heulandite group, mordenite group, faujasite group, laumontite group, pentasil group and the clathrate group. For an overview of zeolite science and the preparation of zeolite molecular sieves, one may wish to refer to Denkewicz R. P. (1987), "Zeolite Science: An Overview," from Jrnl. Mater. Ed., 9(5) and Breck, D. W. (1984), Zeolite Molecular Sieves, R. E. Krieger Publishing Co., Malabar, Fl., both incorporated herein by reference. In terms of zeolites, however the present invention is concerned with the faujasite group and LTA structures zeolites which include principally the X, Y, and. These zeolites are distinguished from other types of zeolites and from each other on the basis of their silica-to-alumina ratio, on the basis of their basic building block structures, as well as on the basis of their physical and chemical properties, etc. The distinction between zeolites of the faujasite group and those of other groups are well known to those of skill in the art as exemplified by the review references discussed above, and include frameworks based on polyhedral cages of cubic or near cubic symmetry.
Molecular sieves which are not zeolitic in nature, i.e., contain framework constituents other than or in addition to Si and Al, but which do exhibit the ion exchange and/or adsorption characteristics of the zeolites, are also known. For example, metallorganosilicates which are said to possess ion-exchange properties, have uniform pores and are capable of reversibly absorbing molecules, are reported in U.S. Pat. No. 3,941,871, issued Mar. 2, 1976, to Dwyer et al. Furthermore, molecular sieve materials having a microporous 3-dimensional crystalline aluminophosphate phase and said to have uniform pore dimensions, are described in U.S. Pat. No. 4,310,440, issued Jan. 12, 1982, to Wilson et al.
An important aspect of molecular sieve chemistry is an ability to modify their structure to incorporate metal chelates, which serves to modify their physical properties, and, hence, their utility. The modification of zeolites can take a variety of forms ranging from simple ion exchange to the encapsulation of large metal clusters. The term "ship-in-a-bottle" complex has been used to describe encapsulated complexes that are too large to escape through the sieve pores. Such complexes can be viewed as a bridge between homogenous and heterogenous systems since neutral complexes would be free to move within the confines of the sieve's cavities but still be trapped within the solid support.
Three different methods have been described for encapsulating a metal complex within certain types of zeolites. Two approaches which have been extensively studied include the flexible ligand and template synthesis approach. The flexible ligand approach, described, e.g., by Herron, N. (1986), Inorg. Chem., 25:4714, involves employing a ligand that when uncomplexed can easily diffuse into the zeolite but once complexed to a metal ion, becomes too large to exit. In contrast, the template synthesis approach, described, e.g., by Meyers et al. (1984), Zeolites, 4:30, involves constructing a large chelate ligand inside the cage from ligand precursors that are small enough to diffuse into the cavity. Lastly, the zeolite synthesis approach described in the present disclosure, the zeolite or molecular sieve is actually synthesized around the metal complex.
While the flexible ligand approach provides certain advantages, including entrapment and site isolation of metal complexes, it is also beset by many problems and disadvantages. Most importantly, the type of metal chelate which one employs must be selected such that in its uncomplexed state it includes a flexible ligand of a shape which can diffuse through openings into the interior of the zeolite, and, after complexing, must have a changed shape such that the complexed ligand cannot exit the interior of the molecular sieve. Additional problems with the flexible ligand approach include incomplete complexation of exchanged metal ions and partial coordination of the ligand.
The template synthesis approach also has certain associated advantages and disadvantages. For example, while this approach has the advantage of entrapment and site isolation of metal complexes, it has the severe disadvantage in that one is quite limited in terms of the type of chelate which can be successfully synthesized within the interior of the zeolite or molecular sieve.
The disadvantages of the template synthesis approach can be appreciated when one considers the encapsulation of metallophthalocyanines (MPc). This has been accomplished in X and Y type zeolites using a template synthesis, and generally involves the diffusion of four dicyanobenzene molecules into the supercage where they condense around a metal ion that was previously exchanged into the zeolite. Problems with this method arise because the synthesis requires temperatures of 150.degree.-400.degree. C. which may result in the reduction of certain metal ions. Additionally, a percentage of the exchanged metal ions may remain uncomplexed.
A third approach which has been attempted in only certain limited circumstances, termed the zeolite synthesis approach, involves the synthesis of a zeolite around the metal chelate complex. While the zeolite synthesis approach could offer certain advantages, its use has only been reported in quite limited circumstances. Moreover, the results to date have been somewhat disappointing. For example, U.S. Pat. No. 4,388,285 to Rankel, et al. discloses the use of a series of transition metal complexes as templates for the synthesis of ZSM-5-type zeolites. This process is carried out by mixing a suitable source of silica, a source of alumina, a source of alkali metal, and at least one transition metal complex. These materials are then reacted at temperatures and under conditions appropriate for the formation of a ZSM-5-type zeolite, followed by crystallization of the resultant zeolite therefrom. Unfortunately, the resultant material was found to be either amorphous (i.e., noncrystalline), or exhibited crystalline purity of on the order of only 5%-50%. Moreover, it does not appear as though the metal chelate was actually encapsulated into the ZSM-5-type zeolite in that although the patent indicates that these complexes were stable to washing by solvent extraction, the present inventor has found that ZSM-5 zeolites incorporating copper phthalocyanine prepared by the method of this patent are not stable to sublimation.
A related patent, U.S. Pat. No. 4,500,503 also to Rankel, et al., discloses what appears to be similar process, but is limited to the preparation of a mordenite-type zeolite. As with the '285 patent, the mordenite which was prepared was either amorphous or had a crystalline purity of only 15-40%. Furthermore, as with the '285 patent, this disclosure is limited to the use of only a few types of metal chelate complexes.
Accordingly, there remain a variety of disadvantages associated with the preparation of zeolites which have metal chelate complexes incorporated within their interior cavity. Foremost among these disadvantages are restrictions upon the types of metal chelates which may be successfully employed. The ability to provide zeolites encapsulating a wide range of possible metal chelate complexes is particularly important where one desires to prepare molecular sieves having a wide range of potential application. Additionally, the types of molecular sieves which contain encapsulated metal complexes have heretofore been limited to molecular sieves of the ZSM-5 and mordenite-type zeolite, and these preparations have themselves been of questionable purity. Accordingly, there is a need for new methods for preparing molecular sieves having encapsulated metal complexes.